1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device including a fuse element that can be cut for changing a circuit configuration of the semiconductor device, and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
In manufacturing a semiconductor device, after a wafer manufacturing process called a front-end process is finished, there is a process of changing a circuit configuration of a semiconductor device by cutting a fuse element formed of, for example, polysilicon or metal by using, for example, a laser, which occupies part of a back-end process. In this process, a resistance value can be corrected to obtain desired characteristics after electrical characteristics of the semiconductor device are measured. This process is thus an effective manufacturing process particularly for semiconductor devices that place emphasis on their analog characteristics.
In this process, it is required for the fuse element to be stably cut by the laser and have a high corrosion resistance. Hitherto, an insulating protective film is formed on an upper portion of a semiconductor device, and, for example, a silicon nitride film is used for the purpose of preventing moisture from coming in from the outside and other purposes. However, a fuse element is assumed to be cut later by laser radiation, and thus, a sufficiently thick silicon nitride film cannot be formed thereon. This is because a silicon nitride film is mechanically robust and is not easily broken by laser radiation simultaneously with the fuse element. Accordingly a protective film above the fuse element is, in general, removed, and thus, the protective film is absent above the fuse element. Further, an insulating film under the protective film is removed as well so as to have a desired thickness suitable for cutting the fuse element, and thus, only an insulating film that is mainly an oxide film for separating wiring layer slightly remains on the fuse element. The fuse element is liable to be affected by incoming moisture, and it is necessary to improve corrosion resistance thereof.
In Japanese Patent Application Laid-open No. 2011-49252, there is proposed a method of improving a corrosion resistance by forming a moisture-resistant insulating film such as a silicon nitride film or a silicon oxynitride film on at least a side surface of a fuse element, or on the side surface and an upper portion of the fuse element in such a manner that the moisture-resistant insulating film is thinner on the upper portion than on the side surface.
However, the above-mentioned related art has the following problems. Although moisture basically enters from a portion above the fuse element from which the protective film is removed, in the method, no moisture-resistant insulating film is formed or the thin moisture-resistant insulating film is formed on the upper portion of the fuse element. As a result the protection of the upper portion is insufficient. Further the use of the silicon nitride film or the silicon oxynitride film as the moisture-resistant insulating film results in strict conditions for cutting the fuse element because the radiated laser beam is absorbed by the film. In this method, the moisture-resistance improvement and the stability of cutting the fuse element by the laser have a trade-off relationship, and hence obtaining conditions that satisfy both the requirements are difficult to achieve. This is because the related-art configuration focuses only on an uncut fuse element and has no effect on a fuse element cut by the laser. When the fuse element is cut, the fuse element is exposed from the cut surface to cause corrosion. The fuse element is corroded from the cut surface and the fuse element thus expands, resulting in cracking of the insulating film formed on the fuse element. Further, a problem arises in that the crack becomes an entering route of the moisture, and hence the corrosion progresses inside the semiconductor device.